The invention relates to a method and apparatus for actuating a vehicle occupant protection device in a vehicle having a sensor system which senses driving state data, and a reversible vehicle occupant protection means that can be triggered and moved into an effective position before a collision occurs.
For example, emergency braking, skidding of the vehicle or an imminent collision is understood to be a critical driving situation or a critical driving state. In such critical situations, preventive measures for vehicle occupant protection are activated and deactivated (that is, are reversed when the danger is passed).
In addition to customary restraint systems such as airbags and seat belts with a seat belt tensioner, there are a series of further controllable vehicle occupant protection systems in vehicles which have a restraining and/or energy-absorbing effect to protect a vehicle occupant in the event of a collision. Examples of such vehicle occupant protection systems are movable impact bodies, cushions and head rests whose size, hardness, shape and position can be changed by means of an actuation. In addition to these vehicle occupant protection systems, it is possible to provide further actuatable protection devices which reduce the consequences of an accident for a vehicle occupant by positioning the vehicle occupant; that is, he or she is placed in a position that is favorable in terms of an accident. Devices for positioning the vehicle occupant are, for example, an electric seat adjustment system, a head rest adjustment system, a seat belt pretensioner and movable upholstered elements.
When actuating the vehicle occupant protection system to reduce the consequences of an accident in road traffic, it is possible to differentiate between preventive measures, which are taken before an accident, and acute measures, which are taken after an accident has been detected. The invention relates in particular to actuation of a protection device as a preventive measure, i.e., as a preventive protection measure.
German patent document DE 101 21 386 C1 discloses a method for actuating a reversible vehicle occupant protection systems in a motor vehicle having a driving state sensor system which senses driving state data, and having a reversible vehicle occupant protection system that can be triggered before the collision time, and as a result moved into an effective position. The driving state data is monitored with regard to a state of “emergency braking”, and when such a state is determined the vehicle occupant protection systems is activated. The data processing device additionally identifies a state of “oversteering” and a state of “understeering”. If either of these states is detected by the data processing device, the reversible vehicle occupant protection system is actuated. After the critical driving state has passed, the actuated vehicle occupant protection system is deactivated.
The braking deceleration which is necessary for emergency braking is usually determined by a surroundings sensing system (for example, a radar unit), an ultrasonic sound measuring unit or an optical sensing unit. In this context, the presence of a critical situation, in particular an imminent collision, is determined by means of the distance from an obstacle and the relative speed with respect to said obstacle.
German patent document DE 36 37 165 A1 or DE 101 21 956 C1 discloses a method for actuating a vehicle occupant protection system for a vehicle in which an obstacle in front of the vehicle can be detected by a surrounding and/or distance sensor system. When an obstacle is detected, a braking deceleration that is necessary to bring the vehicle to a standstill before striking the obstacle is determined and compared with a maximum possible braking deceleration. A vehicle occupant protection system is activated as soon as the necessary braking deceleration exceeds the maximum possible braking deceleration.
German patent document DE 102004018394.5, which was published after the present application, discloses a method comparable to that described above, in which the necessary braking deceleration is not determined, or it is not evaluated (in terms of its exceeding a threshold) until a driver of the vehicle has activated a brake activation element for initiating a braking process.
One object of the invention is to provide an improved method and a device of the type described above, in which the preventive triggering of vehicle occupant protection means is felt by the driver to be as plausible as possible.
This and other objects and advantages are achieved by the method according to the invention, in which a setpoint braking deceleration is determined by a predictive surroundings sensing unit. In particular, the surroundings sensing unit determines the presence of at least one critical driving state, and if such a driving state is present the vehicle occupant protection means is activated. The setpoint braking deceleration is checked using a deceleration characteristic curve which is dependent on vehicle speed, and the vehicle occupant protection means is activated if the determined requested braking deceleration is above the deceleration characteristic curve.
A reversible vehicle occupant protection device is a device whose purpose is to reduce the force loading on a vehicle occupant in the case of a collision. In this context, the protection device can be changed repeatedly from an initial state to an effective state by activation, and be reset again to the initial state from the effective state by deactivation. For example an electric seat adjustment device, a reversible seat belt tensioner, an electric adjustment device for vehicle openings, a head rest adjustment means, or a movable upholstered element are activated as reversible vehicle occupant protection systems. Electrically adjustable impact protection devices can also be considered to be reversible vehicle occupant protection devices in the sense of the invention, and these can also comprise, for example, reversibly deployable engine hoods or extendable bumpers whose aim is predominantly to protect pedestrians.
The advantage of the method according to the invention is that the setpoint braking deceleration which is predefined (for example, by a radar system taking into account the distance and relative distance to the obstacle), can be checked by referring to further conditions which reflect the criticality of the driving situation and its perception by the driver, and can be used for more differentiated actuation of a reversible vehicle occupant protection means. In this way, the vehicle occupant protection means is activated only if the activation is also perceived as plausible for the respective driving situation by the driver. In particular, the subjective sensation of the driver with regard to braking decelerations is dependent on the driving speed.
When the predefined or requested setpoint braking deceleration is checked, it is possible to achieve coordination with the subjective sensation of the driver by means of the deceleration or acceleration characteristic curve which is dependent on the vehicle speed (such subjective sensation being dependent, inter alia, on the driving speed). In the text which follows, “deceleration” refers to the absolute value of a negative acceleration of the vehicle during braking.
In one advantageous embodiment, in a speed range above a threshold of approximately 60 km/h, the deceleration characteristic curve (which corresponds to a critical braking deceleration) drops continuously to a base absolute value. The assumed reduction in the deceleration characteristic curve at high speeds, and the more sensitive activation of the vehicle occupant protection means which is coordinated therewith, is felt by the driver to be plausible since at a high driving speed the subjective sensation of the driver perceives the braking decelerations in a more critical way.
As a further condition for influencing the deceleration characteristic curve, it is possible to differentiate whether an emergency braking process is i) triggered by the driver and supported by a radar-supported braking assistance system, or ii) triggered by a surroundings sensing system without intervention by the driver. In both cases, the necessary setpoint braking deceleration on which the present method is based is determined by the surroundings sensing system, based on the distance from, and speed relative to, an obstacle.
If the emergency braking process is triggered by a driver and is supported by a braking assistance system, a hazardous situation or emergency situation is inferred from the behavior of the driver. For this purpose, at least one parameter such as brake pressure, speed of activation of the brake pedal and the speed with which the acceleration pedal is released are used to evaluate the braking process. In order to calculate the necessary brake pressure, the surroundings sensing unit calculates the necessary setpoint braking deceleration based on the distance from speed relative to the obstacle, in order, if appropriate, to correspondingly correct the brake pressure requested by the driver via the brake pedal.
In the case of a braking process which is triggered by the driver, he or she is already prepared for the hazardous situation, and accordingly a high degree of braking deceleration is consciously perceived and tolerated. The deceleration characteristic curve for the critical braking deceleration is therefore above a deceleration characteristic curve for an autonomous partial braking process in which a driver is surprised by an autonomous braking process, and may or may not be taking avoidance measures before the obstacle.
For example, as shown in FIG. 2, in the case of a braking process which is triggered by the driver in a lower speed range of 0 km/h to 60 km/h, a setpoint braking deceleration of up to 10 m/s2 which is predefined by the surroundings sensing unit is still considered to be controlled and acceptable. Accordingly, it is still not necessary to trigger any vehicle occupant protection system, even if the loading in the limiting range is already felt to be at a maximum by the driver. This high threshold for the critical braking deceleration is felt to be plausible by the driver because triggering of a vehicle occupant protection system would be perceived as unnecessary. Moreover, in the case of a setpoint braking deceleration of up to 10 m/s2 which is predefined by the surroundings sensing unit, it is still possible to avoid a collision because such high braking deceleration can be reliably applied by a vehicle brake system when there is a coefficient of friction of μ=1.0. Since no collision is expected, triggering of the vehicle occupant protection means would be implausible. However, if the real deceleration is actually too low, in the next step the setpoint braking deceleration would be increased by the surroundings sensing unit, so that the deceleration characteristic curve is exceeded and the vehicle occupant protection means is triggered.
In a medium speed range of 60 km/h to 120 km/h, a reduction of the critical braking deceleration from 10 m/s2 to at least 8 m/s2 is accepted. In an upper speed range (higher than 120 km/h), a critical braking deceleration of approximately 8 M/s2 is accepted. The accepted reduction in the critical braking deceleration at high speeds and the more sensitive activation of the vehicle occupant protection means which is coordinated therewith is perceived as plausible by the driver, because braking deceleration at relatively high driving speeds is perceived to be more critical. On the other hand, the threshold which is selected is still so high that no undesired triggerings occur. For example, in the case of a “sporty” targeted braking carried out intentionally by the driver, for example to avoid a stationary obstacle, the braking deceleration is usually in the region up to a maximum of 7 M/s2.
In the case of an autonomously triggered braking process, the deceleration characteristic curve is to be configured in a more sensitive way, which could be done by adapting the curve parameters of the deceleration characteristic curve described above. For example, the cut-off values for the critical braking deceleration could be reduced to 3.5 M/s2 and 1.5 M/s2. The speed ranges could also be defined by cut-off values of 50 km/h and 150 km/h (FIG. 3).
In a further embodiment the vehicle occupant protection is actuated only if the vehicle speed is higher than a predefined minimum. For example, 30 km/h is predefined as a minimum speed, and the vehicle occupant protection is activated only starting from a vehicle speed higher than 30 km/h. This condition can be interrogated separately or can be implemented by means of a suitable critical deceleration characteristic curve which assumes an unattainable high value below the minimum speed.
In various embodiments the deceleration characteristic curve can additionally be varied as a function of other parameters.
The braking deceleration which is determined by one of the predictive surroundings sensing units (for example a radar unit, an infrared inter-vehicle distance measuring device, an ultrasonic sensor or a camera) represents a setpoint braking deceleration which is necessary to avoid a collision. In order to determine the setpoint braking deceleration necessary to avoid a collision, a coefficient of friction of μ=0.9 of the underlying surface (which corresponds to a dry and normal underlying surface, for example a dry asphalted underlying surface) is typically assumed. In one development, in order to take into account the different states of the underlying surface and the differing adhesion, it is possible to predefine the deceleration characteristic curve as a function of a coefficient of friction for the underlying surface which is obtained, for example, by a sensor. For example, different deceleration characteristic curves can be stored as a function of the state of the road (such as a cobbled road, a country road or a freeway), and they can be correspondingly activated when the road is traveled on. This requires the state of the road to be determined in advance. Suitable methods are known from the prior art.
Calculation of the setpoint braking deceleration based on a permanently predefined coefficient of friction of μ=0.9 leads, (particularly in the case of smooth road conditions) to unrealistic results: when braking hard on a smooth (for example, wet) underlying surface with a very low coefficient of friction, the wheels would no longer grip and roll but would instead slide, which can lead to locking of the wheels. A setpoint braking deceleration which is predefined by the radar system when the vehicle approaches an obstacle, and which would still be below the deceleration characteristic curve, would not be uncritical in any way because it would in fact be completely impossible to apply the setpoint braking deceleration, due to the actual low coefficient of friction.
In the text which follows, a method is described for remedying this deficiency in a simple and cost-effective way. This applies generally to any method for triggering vehicle occupant protection systems which are based on an evaluation of the setpoint braking deceleration on which an assumption of a constant coefficient of friction is made. The interrogation (low μ interrogation) takes place in a parallel triggering path.
For a braking process with intervention of an antilock brake system ABS (ABS situation), immediate activation of the vehicle occupant protection system occurs in a simple embodiment. This is appropriate, for example, for a case in which the predictive surroundings sensing unit detects a collision which cannot be avoided and predefines a maximum braking deceleration (emergency braking) which still serves only to reduce kinetic energy in advance of the collision. It is then in fact certain that the grip limit is exceeded and the braking deceleration which is available is never sufficient to prevent an accident. For this reason, any additional interrogation is superfluous.
For a case of partial braking with intervention of the ABS (ABS situation), in which there could still be the possibility of avoiding an accident, it is, however, necessary to check in a further interrogation how great the actual longitudinal deceleration of the vehicle is in order to obtain an indication of the braking effect which is occurring. When an ABS intervenes, braking is always carried out to the limiting value of the coefficient of friction so that in this situation the coefficient of friction is directly correlated to the longitudinal deceleration of the vehicle and could be derived therefrom. In order to check whether a critical state is present in which a collision would no longer be avoidable due to the reduced coefficient of friction, a coefficient (μ) of friction of less than 0.5 is considered critical. For this reason, in the ABS situation the longitudinal deceleration of the vehicle is determined and is compared with a predefined threshold value or limiting value of, for example, 5 m/s2. If the vehicle longitudinal deceleration drops below this threshold value (i.e., if the longitudinal deceleration of the vehicle is, for example, only 4 m/s2), this is due to the inadequate grip of the covering of the underlying surface. Thus, the vehicle occupant protection means is activated, because adequate setpoint braking deceleration could never be achieved and an accident is very probable.
The deceleration characteristic curve for the setpoint braking deceleration is reduced as a supplementary measure for making available better preventive protection in boundary situations in terms of vehicle movement dynamics if the ABS or generally a vehicle movement dynamics control system is activated for a predefined time period. For this purpose, the vehicle movement dynamics control system is monitored for activation. In the process it is checked whether the vehicle movement dynamics control system is actuated for a predefined time period of, for example, at least 0.15 sec. If so, facilitated triggering of preventive measures is achieved with the reduction of the deceleration characteristic curve by virtue of the fact that the deceleration characteristic curve can be more easily exceeded by the setpoint braking deceleration which is predefined by the radar system. This is appropriate in particular in conjunction with the interrogation, described above, for a low coefficient of friction (low μ), which activation of the ABS requires.
Different vehicle movement dynamics control systems (for example an antilock brake system ABS, an electronic braking force distribution means EBV, an electronic stability program ESP, a traction controller ASR) are expediently monitored in parallel for activation of, for example, at least 0.1 sec.
Alternatively or in an additional condition it is possible to compare, instead of the setpoint braking deceleration, a variable derived from the setpoint braking deceleration, with a corresponding characteristic curve which is modeled on the deceleration characteristic curve. For example, by means of a vehicle model, it is possible to determine from the setpoint braking deceleration predefined by the radar system a setpoint braking torque said setpoint braking torque being required to determine the brake pressure which is predefined to the wheels, in order to make a decision about the triggering of vehicle occupant protection system using a braking characteristic curve that is dependent on vehicle speed. These derived variables are also to be understood as being included in the term “setpoint braking deceleration”, unless they differ explicitly therefrom, as in the following exemplary embodiment.
The setpoint braking torque follows the setpoint braking deceleration with a delay, which corresponds to the effect of a low-pass filter. In one embodiment, the vehicle occupant protection means is actuated only if the necessary setpoint braking torque is (also) above a braking characteristic curve. Activation of the vehicle occupant protection system as a function of the predefined setpoint braking torque ensures that, when autonomous partial braking occurs with moderate setpoint braking deceleration (no emergency braking), the vehicle occupant protection system is not activated until after the start of braking. Accordingly, connection into the circuit does not occur until the driver has already been prewarned by the autonomous partial braking.
A similar effect can be achieved if it is ensured by a corresponding interrogation of a timer that the vehicle occupant protection means is not triggered until after the expiration of a time period of, for example, 400 ms from the activation of the autonomous partial braking.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.